Most of the existing Light Emitting Diode (LED) luminaries have the structures which is designed based on the conventional gas discharge lamp and Tungsten lamp. The driving scheme which follows the conventional idea includes: providing one driver for one light source, and using a conventional AC/DC conversion technique with single-path or multi-path output. As shown in FIG. 1, a lighting device includes a light source and a driver, and is controlled by a distribution switch. As shown in FIG. 1, the driver is provided nearby the light source inside the lighting device.
Specifically, FIG. 2 shows a circuit structure of an LED lighting device. In FIG. 2, a output voltage adjustable voltage source 201 in the front-stage samples the minimum value of the drain voltages of adjustment transistors Q1˜Qn in the multi-path linear adjustment current-limiting circuit 203 in the post-stage via a minimum value sampling circuit 202, and a feedback control is performed based on the minimum value by an output voltage control circuit 204. In this way, the minimum value is kept to a small value, and the output voltage Vo of the output voltage adjustable voltage source 201 is always little larger than the voltage of the LED load with the highest voltage in the multi LED loads, and thus the linear adjustment current-limiting circuit 203 always has the minimum power consumption approximately while ensuring that the constant current driving of the current limit is performed by each LED load. The driver of the lighting device includes the output voltage adjustable voltage source 201, the minimum value sampling circuit 202 and the output voltage control circuit 204; and the light source unit includes a multiple of LED compositions and a multiple of linear adjustment current-limiting circuits (a LED branch includes a LED composition and a corresponding linear adjustment current-limiting circuit).
However, the above circuit structure has the following disadvantages.
Firstly, in order to facilitate the minimum value sampling circuit of the driver to perform a voltage sampling from the post-stage circuit, the linear adjustment current-limiting circuit 203 of each LED branch often needs to be enclosed inside the driver, the loss of the adjustment transistor is large when the voltage difference between the multiple of LED branches is large, resulting in serious heat of the driver. Moreover, the driver is generally placed nearby the LED light source inside the LED lighting device, thus the temperature thereof will be higher, which affects the reliability of the driver seriously.
Secondly, the output voltage control circuit 204 of the output voltage adjustable voltage source 201 in the front-stage needs to sample the voltage of the post-stage circuit composed of a LED and the corresponding linear adjustment current-limiting circuit 203, so that the wiring between the front-stage output voltage adjustable voltage source 201 and the post-stage circuit is complicated. Moreover, when an open circuit fault occurs in a certain LED load, the drain voltage of the linear adjustment transistor is zero. Therefore, it is necessary to further provide an open circuit protection for each LED load, so as to ensure that other LED loads in which no fault occurs can operate normally in this case, which further increases the complexity of the circuit.